Effects of intra and interspecific interactions on the survival of two predatory ladybirds (Coleoptera: Coccinellidae) in relation to prey abundance

Abstract

The relative effects of intra and interspecific interactions on the larval survival of two species of aphidophagous ladybirds, Coccinella septempunctata brucki and Harmonia axyridis, were assessed at two different prey abundances. In single species rearing, the number of larvae of both species decreased during the latter developmental stages, mainly due to cannibalism. When prey was abundant, the survival of both species improved; however, in mixed species rearing, the mortality of C. septempunctata brucki due to cannibalism or intraguild predation was higher than in single species rearing, whereas the mortality was lower in H. axyridis. Consequently, the survival of C. septempunctata brucki decreased while that of H. axyridis improved. In addition, in the 18 intraguild predation events observed, H. axyridis was always the intraguild predator and C. septempunctata brucki was its prey. Thus, when these two species co-exist in the field, H. axyridis is likely to be an important intraguild predator of C. septempunctata brucki. In addition, when prey is scarce, it is likely that cannibalism and intraguild predation become more important factors in the intra and interspecific relationships of these two species.